In a production well, a production string composed of the production tubing and other completion components is used to transport production fluid containing hydrocarbons from a downhole formation to the surface of the well. This production tubing is typically pressure tested to insure that no leaks will form under the pressure of actual production. It is desirable to find leaks before production fluid is introduced into the tubing because of the gross inefficiencies of post-production repair. Typically, a temporary well barrier, or temporary plug, is used to seal off a particular segment of the production tubing, or well zone, for pressure testing. Often, the well zone consists of essentially the entire well. Fluid is then introduced above the temporary well barrier and pressurized to detect leaks. After testing, the temporary well barrier must be removed from the production string.
Several types of well isolation devices using temporary well barriers exist in the prior art, including the Model E Hydro Trip pressure sub by Baker Oil Tools, the OCRE Full Bore Isolation Valve and Multi-Cycle Tool by Baker Oil Tools, and the Mirage Disappearing Plug from Halliburton. While some well isolation devices use valves to control well flow, it is often desirable that once the temporary well barrier is removed, substantially the full inner diameter of the production tubing is restored. One type of temporary well barriers typical of the prior art include solid barriers held in place by a support assembly. To remove the barrier, the support assembly is retracted or sheared off to allow the solid barrier to drop through the wellbore. Designs relying on gravity for removal of the plug, however, have limited applications in substantially horizontal wells.
To extend well-isolation to horizontal wells, plugs were developed that provide a large bore in the well isolation device after removal of the temporary well barrier without dropping the temporary barrier into the wellbore. These plugs are broadly referred to as disappearing plugs. One type of disappearing plug operates by recessing the temporary well barrier into the housing of the well isolation device. One disappearing plug from Baker Oil Tools, for example, recesses a flapper into the tool where it is isolated from the production flow path.
Other disappearing plugs operate by disintegrating a frangible well barrier, typically by impacting the barrier or setting off an explosive charge. Total Catcher Offshore AS in Bergen has developed several well isolation devices employing this type of plug, such as the Tubing Disappearing Plug (TDP), the Tubing Disappearing Smart Plug (TDSP), and the Intervention Disappearing Smart Plug (IDSP).
U.S. Pat. No. 6,026,903 by Shy et al. describes a bidirectional disappearing plug which is capable of selectively blocking flow through a flowbore of a tubing string disposed within a subterranean well. The plug may subsequently be disposed of, leaving little or no restriction to flow through the flowbore, and leaving no significant debris in the flowbore by causing a rupture sleeve to penetrate the plug member and destroy the plug's integrity.
The aforementioned disappearing plugs currently in use, while an improvement over previous technology, are less than ideal because they lack reliability, especially in environments where wells deviate from vertical.